A quantitative assessment of the sensitivity of whole-head MEG to activity in the adult human cortex
A quantitative assessment of the sensitivity of whole-head MEG to activity in the adult human cortex
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DOI：
10.1006/nimg.2002.1102
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发表时间：
2002-07-01
期刊：
影响因子：
5.7
通讯作者：
Barnes, GR
中科院分区：
文献类型：
--
作者：
Hillebrand, A;Barnes, GR
脑磁图（MEG）依赖于通过测量头部外部的相关磁场来检测皮层电流。这个磁场的幅度很大程度上取决于脑电活动的深度。此外，径向取向的源在同心均匀体积导体中是磁性沉默的，从而引起了MEG对深源和回旋源都不敏感的传闻假设。利用从两个成年人大脑的磁共振图像（MRI）中提取的皮质表面，我们构建了所有可能的单源元素，并检查了实际上可以用全头MEG系统检测到的活跃新皮质的比例。我们确定了那些电活动区域，MEG是最敏感的分析计算的概率在指定的置信体积内检测到一个源。我们的研究结果表明，源的深度，而不是方向，是主要因素，妥协的敏感性，脑磁活动在成年人的大脑皮层。在脑回顶部存在分辨率较差的细条（宽度约为2 mm）;然而，这些细条仅占皮质区域的相对较小比例，并且由于其靠近传感器阵列，因此被具有标称切向分量但分辨率较高的元素包围。最后，我们改变了皮层活动的补丁的程度，表明小补丁有一个小的净电流矩，因此不太明显，而大补丁有一个强大的净电流矩，通常是更明显的脑磁图系统，但不太适合建模为单偶极子。(C)2002 Elsevier Science（美国）。
MagnetoEncephaloGraphy (MEG) relies on the detection of cortical current flow by measurement of the associated magnetic field outside the head. The amplitude of this magnetic field depends strongly on the depth of the electrical brain activity. Additionally, radially orientated sources are magnetically silent in a concentrically homogeneous volume conductor, giving rise to the anecdotal assumptions that MEG is insensitive to both deep and gyral sources. Utilising cortical surfaces extracted from Magnetic Resonance Images (MRIs) of two adult brains we constructed all possible single source elements and examined the proportion of active neocortex that is actually detectable with a whole-head MEG system. We identified those electrically active regions to which MEG is maximally sensitive by analytically computing the probability of detecting a source within a specified confidence volume. Our findings show that source depth, and not orientation, is the main factor that compromises the sensitivity of MEG to activity in the adult human cortex. There are thin strips (similar to2 mm wide) of poor resolvability at the crests of gyri; however, these strips account for only a relatively small proportion of the cortical area and are abutted by elements with nominal tangential component yet high resolvability due to their proximity to the sensor array. Finally, we varied the extent of the patches of cortical activity, showing that small patches have a small net-current moment and are therefore less visible whereas large patches have a strong net-current moment, are generally more visible to the MEG system, yet are less appropriately modelled as single dipoles. (C) 2002 Elsevier Science (USA).